Anionic polymerization techniques have been used to synthesize polymers that are useful in the manufacture of tire components. As is known in the art, certain initiators can be used that impart a functional group to the “head” of the polymer. And, certain terminating agents can be used that impart a functional group to the “tail” of the polymers. These functional groups are believed to have a beneficial impact on the performance of the polymers. For example, certain functional groups can yield lower hysteresis in reinforced rubber vulcanizates prepared using the functionalized polymers.
Telechelic linear polymers include a functional group at each terminus of the polymer (i.e., at the head and tail of the polymer). The polymers are believed to provide advantages deriving from the presence of a functional group at each terminus. These telechelic polymers have generally been synthesized by one of two routes. First, a functional initiator can be employed to initiate polymerization followed by the use of a functional terminator. While the ability to impart a functional group to the tail of a polymer through the use of a functional terminator is generally efficient, difficulties are often encountered when employing functional initiators and therefore lower yields of telechelic polymers are often observed when practicing this technique. A second technique includes the use of divalent initiators such as dilithio compounds. These initiators can produce diliving polymers that can be terminated with functional terminators to produce telechelic polymers. With regard to the latter, the ability to produce linear, high molecular weight polymer having narrow molecular weight distribution has proven to be problematic. It is believed that the lithium atoms of the dilithio initiators tend to aggregate and thereby have a deleterious impact on the polymerization. In order to alleviate these problems, U.S. Patent Publication No. 2009/0326176 proposes the use of multi-functional lithiated amine-containing initiators to produce diliving polymers.
While multi-functional lithiated amine-containing initiators have proven useful and overcome many of the problems associated with prior multi-valent lithiated initiators, there remains a desire for multi-valent lithiated initiators that are stable in aliphatic and/or cycloaliphatic solvents and remain stable during polymerizations including continuous polymerizations and polymerizations conducted at higher temperatures.